9:45 AM - 10:00 AM
[AAS21-09] Impacts of black carbon aging on its spatial distribution and radiative effect in the global scale
Keywords:Aerosol, Black carbon, Global aerosol model, Aging process, Transport, Radiative effects
Recently, Oshima and Koike  developed a new parameterization of BC aging based on the physical and chemical processes. In this parameterization, the conversion rate from hydrophobic BC to hydrophilic BC is expressed as a production rate of condensed materials normalized by the hydrophobic BC mass concentration. In this study, we applied this parameterization to the global-scale aerosol model MASINGAR-mk2 included in the MRI's earth system model [Yukimoto et al., 2012], which enables the representation of spatial and temporal variations of the conversion rate of BC aging depending on atmospheric conditions (the original approach assumed the constant conversion rate of 1.2 days).
We performed the model calculation with the BC aging parameterization for 2008-2009. We find that the conversion time scales from hydrophobic BC to hydrophilic BC exhibit distinct spatial variations and they were approximately one day and one week over the source regions in East Asia and the remote regions in the Arctic, respectively. We also performed the model calculation with the constant conversion rate (1.2 days) for the comparison. Over the source regions in East Asia, both calculations give small differences in BC mass concentrations and they reproduced the seasonal variations of BC mass concentrations observed by the surface measurements reasonably well. On the other hand, the both calculations give large differences in BC mass concentrations over the Arctic regions and the calculation with the parameterization improved the prediction of the BC mass concentration, which was underestimated in the constant-rate calculation.
The direct radiative forcing by BC (annually and globally averaged at the top of atmosphere) was approximately 0.3 W m-2 for the calculation with the parameterization (approximately 0.2 W m-2 for the constant-rate calculation). This result indicates that the aging process of BC in the micro-scale can significantly impact on the spatial distribution and radiative forcing in the global-scale through the parameterization. However, the calculations shown in this study do not take into account the enhancement of BC light absorption due to coatings and they may underestimate the direct radiative forcing. We will introduce model results including the enhancement effect in this presentation.
Oshima, N., and M. Koike (2013), Geosci. Model Dev., 6, 263-282, doi:10.5194/gmd-6-263-2013.
Yukimoto, S., et al. (2012), J. Meteor. Soc. Japan, 90A, 23-64, doi:10.2151/jmsj.2012-A02.